Oscillation circuit



Aug. 24 1926. 1,597,398

L. 1". WILSON OSCILLATION CIRCUIT Filed May 1. 19 O 2 Sheets-Sheet 1 v10 .h, F7

Q70 i J6 2 4 I r 47 K7 Aug. 24, 1926. 1,597,398

-L.. T. Wl LSON OSCILLATION CIRCUIT Filed May 1, 1920 '2 Sheetsl-Sheet 2Z5, Melt/Z37",

Lm. kw,

t amplifying highfrequency currents.

LEONT. WILSON, OF WEST SOMERVILLE, MASSACHUSETTS, ASSIGNOR, lBY MES NEAS- SIGNMENTS, TO POWEL CROSLEY, J 11., OF CINCINNATI, OHIO.

OSGILLATION CIRCUIT.

Application filed May 1,

The resent invention relates to oscillation circuits for radiotransmitting appara; tus and more particularly to such circuits employing thermionic tubes for generating or t is usual in this type ofcircuit to employ a direct current source for supplying energy to theplate and filament circuits. There are certain advantages, however, inutilizing an alternating current source for this purpose and it has beenproposed to employ a multiphase source of alternating current forsupplying energy to the plate and filament circuits, the 'fiuctuationsof energy in the circuits being modulated as desired.

It is the object of the present invention to provide a new formof-oscillating circuit and thermionic tube connected therein which shallpermitthe employment of a single phase alternatingcurrent source ofsupply for both the plate and filament circuits.

The present invention is not only adapted for use in connection withcommercial sources of supply employing a sixty cycle single phasealternating current source of supply, but, in addition, is particularlyadapted for the changing over of spark sets having a motor generator setto transmitting apparatus employing a thermionictube in which the motorgenerator set may be used as the source of supply.

In the drawings, Fig. 1 illustrates an oscillation circuit for radiotelegraphy, Fig. 2 illustrates the embodiment of the invention in. anexisting type of transmitting circuit for radio telephony and Fig. 3illustrates a modification for smoothing out the. platecurrent toa-greater degree.

As shown in Fig. 1, the usualathermionic tube is indicated at 10, thistube being provided with a filament 12, a grid 14L, and two plates 15and 16. The two plates are connected into opposite sides of a platecircuit indicated at 18 which 'is inductively coupled through atransformer 20 with an alternating current source of supply 21, This A.C. source of supply is single phase and may have any desired frequencyaccording to its mode of generation. Connected in series with each ofthe plates 15 and 16 and opposite ends of the transformer "secondary 20are inductances 22 and 23;" In addition,

condensers 24 and 25 are; connected across the plate circuit, asindicated, these condencers thus being in shunt with the plates 1920.Serial No. 378,269.

15 and 16. The grid or control electrode 14 ply current, but owing tothe inductance and capacity in the plate circuit, the pulsations ofcurrent are smoothed out materially, producing' a slightly fluctuatingflow of current which is suitable for undamped wave transmission. Itwill be obvious to those skilled in the artthat in this manner bothhalves of the single phase alternating. wave in the source of supplywill be utilized, as'during one half of'the cycle the plate 15 will bepositive and during the next half of the cycle the plate 16 will bepositive, the inductance 28 in either case being traversed by the platei I current. If it were attempted to apply the alternating source ofsupply directly to the usual plate circuit the resulting plate currentwould be so highly modulated that it would be unsuitable fortransmitting purposes.

It has been found that in some instances the inductances 22 and 23 andcondensers 2e and 25 which serve to smooth out the pulsations of currentin the plate circuit may be omitted. In this case the current in theplate circuit is modulated in accordance with the modulation of thesupply and the inductance 28 connected to the middle point of thesecondary serves to further smooth out the fluctuations in the currentand also insure the continuance of oscillation.

In. order to insulate the plates from one another and aid in the:insulation of the grid from the high voltage of the plate theillustrated embodiment of the invention is provided with condensers 30and 31, which may, if so desired, be designed to fulfill the function ofthe condensers 24 and 25, enabling these condensers to be omitted fromthe circuit. The condensers 30 and 31, as shown, are connected to theusual oscillating circuit 32 and .thus serve to conduct the highfrequency currents from the plate to this circuit. The grid circuit 26is also connected with the oscillating circuit 32 in a manner to bepresently describe-d, thereby forming a coupling between the plate andgrid circuits, by which the oscillations in the plate circuit may be fedback to the grid circuit in the usual manner to set up oscillations inthe circuit 32, the frequency of the oscillations depending upon theelectrical characteristics of the circuit.

As shown, the filament 12 also receives'its energy from the source ofsupply 21 through a circuit 34 inductively ,coupled with the transformerprimary through a secondary 35. This filament current is controlledthrough a variable resistance indicated at 36. In order to render thefilament current more uniform and reduce the modulation, due to the A.C. drop along the filament, an additional resistance 38 is connectedacross the filament and is tapped at approximately its, electricalcenter 39, this tap being connected with the oscillation circuit 32 andthe circuit 27 through a connection indicated at 40. a

The choke circuits indicated at 42 and 43 are for'the purpose ofpreventing the flow of radio frequency currents through the condensers24 and 25 or the secondary of the transformer 20 supplying the platecurrent. In other words, the choke circuits are for the purpose ofpreventing the short circuiting of the high frequency currents flowingthrough the oscillation circuit 32 and the included condensers 46 and47. The oscillation circuit, as usual, contains the variable condensers46 and 47 and inductance 48 supplying energy to an antenna circuit 50through a second inductance 52 embodied in the antenna circuit. Thechoke circuit o iserves to conveyto the filament the charge whichcollects on the grid during the oscillat on of the circuit and preventsthe short circuiting of the condenser 46. In addition, a condenser 56isrprovided to aid in insulating the grid from the high volt age appliedto the plates. Thiscondenser, for some. reason at present not known,also aids in reducing the undesirable modulation of the output.

It will be obvious to those skilled in the art that although for reasonsof simplicity and because of certain inherent advantages the presentinvention is shown as-applied to a single tube having two platescoopcrating with the usual filament and grid, if so desired the sameresults may be ob tained by the use of two bulbs properly connected inthe circuit and each having a single filament, grid and plate.

Fig. 2 illustrates the application of the present invention to atransmitter circuit for radio telephony. As shown, this circuit isprovided with an oscillator tube 60 and a modulator tube 61, each havingthe filament 12, grid 14, and two plates 15 and 16, the plates in bothtubesreceiving thei r energ from the A. C. source of supply 21.gonnected in series with the plates are the inductances 63, 64 and 65,corresponding the circuit shown in Fig. l. In addition, the inductances63, 64 and 65 are designed as audio frequency chokes which prevent theflow of current in the plate circuit at to the inductances 22, 23 and 28in audio frequency and therefore maintain a substantially constant platecurrent to both tubes. It will be seen that inductance 64 in common withinductance 28 of Fig. 1 is traversed by all the plate currents. Withthis arrangement, the plate current of the modulator tube is increasedand decreased in the usual manner according to the speech frequency orvoltage impressed upon the grid of the modulator tube through atelephone circuit 65, inductively coupled with any undesirablemodulation, due to the A.

C. supply is substantially.eliminated. The usual resistance 70 isconnected across the secondary of the transformer 67 to. stabilize theaction of the transformer and im prove the modulation.

The employment of a vacuum tube as an oscillator or amplifier having amodulated plate current has certain distinct advantages for purposes ofradio tclegraphy as the mod ulated wave emitted by such a transmittergives a steady note with excellent tone qualities which is well adaptedfor reception to the receiving circuits. This note, due to the abovecharacteristics, lends itself to high amplification at the receiving endby the use of the usual regenerative circuits, thus enabling the tubeset to transmit a greater distance, due in partto the use of theregenerative receiving circuit and the reduced interference from otherstations and static disturbances.

For purposes of radio telephony it may be desirable, however, to smoothout the plate current to a greater degree than is possible with thecircuit shown in Fig. 2. To this end the circuit shown in Fig. 3 of thedrawings may be employed. As indicated therein, resistances and 81 aretapped off of the secondary of the transformer 20 at points near itselectrical center, these resistances being connected with separate grids84 and 85 through additional circuits,

indicated at 86 and 87, respectively. The grids 84: and'85 are embodiedin two separate thermionic tubes and each cooperates with a filament 89and plate 90. The connection with the grids is so arranged that thevoltage applied to each grid is Opposite to the voltage applied to thecorresponding plate,

tending to smooth out the plate current to a certain extent. In additionto the modulation of the plate current afiorded by the usual inductances22, 23 and 28 and the condensers 24 and 25, as shown in Fig. 1, locatedin each of the circuits 86 and 87 is inductance and capacity indicatedat 92 and 93, respectively. This inductance and capacity is designed tochange the phase of voltage applied on the grid so that it may be madeopposite to the pulsations of plate current. By properly varying thephase and amplitude of the voltage applied to the grids, the pulsationsof plate current may be entirely smoothed out and a steady flowobtained. a

ll claim:

1. An oscillation circuit comprising a plate circuit including twoplates, a cathode circuit having provision for electron em ssion towardthe plates, a grid circuit for controlling the flow of electrons betweenthe cathode circuit and the plates, and connections to the plate circuitenergizing means for impressing on the grid circuit variations involtage opposite to and of smaller magnitude than those impressed on theplate circuit.

3. An oscillation circuit comprising a plate circuit including twoplates, a cathode circuit for controlling the flow of electrons betweenthe cathode circuit and the plates. a transformer adapted to have itsprimary connected to a source of alternating currentand having itssecondary connected to the plate circuit to cause each plate to carryalternate halves of the induced wave, and grid circuit connections forimpressing upon the grid circuit a voltage which is opposite to thevoltage applied to the plate circuit to smooth out pulsations in theplate circuit.

-'4. An oscillation circuit comprising a plate circuit including twoplates, a cathode circuit, a grid circuit, a transformer adaptedto haveits primary connected. to an alternating source and having the ends ofits secondary connected with the plates, and means tit for tapping thegrid circuit into the secondary of the transformer in such a manner thatthe voltage in the grid circuit is opposite to the voltage applied totheplate circuit.

Leon r. wrnson

